Pollen competition between morphs in a pollen‐color dimorphic herb and the loss of phenotypic polymorphism within populations

Flower color polymorphism is relatively uncommon in natural flowering plants, suggesting that maintenance of different color morphs within populations is difficult. To address the selective mechanisms shaping pollen‐color dimorphism, pollinator preferences and reproductive performance were studied over three years in Epimedium pubescens in which some populations had plants with either green or yellow pollen (and anthers). Visitation rate and pollen removal and receipt by the bee pollinator (Andrena emeishanica) did not differ between the two color morphs. Compared to the green morph, siring success of the yellow morph's pollen was lower, but that of mixtures of pollen from green and yellow morphs was lowest. This difference, corresponding to in vivo and ex vivo experiments on pollen performance, indicated that pollen germination, rather than tube growth, of the green morph was higher than that of the yellow morph and was seriously constrained in both morphs if a pollen competitor was present. A rare green morph may invade a yellow‐morph population, but the coexistence of pollen color variants is complicated by the reduced siring success of mixed pollinations. Potential pollen competition between morphs may have discouraged the maintenance of multiple phenotypes within populations, a cryptic mechanism of competitive exclusion.     

Pollen colour morphs take different paths to fitness

Colour phenotypes are often involved in communication and are thus under selection by species interactions. However, selection may also act on colour through correlated traits or alternative functions of biochemical pigments. Such forms of selection are instrumental in maintaining petal colour diversity in plants. Pollen colour also varies markedly, but the maintenance of this variation is little understood. In Campanula americana, pollen ranges from white to dark purple, with darker morphs garnering more pollinator visits and exhibiting elevated pollen performance under heat stress. Here, we generate an F2 population segregating for pollen colour and measure correlations with floral traits, pollen attributes and plant‐level traits related to fitness. We determine the pigment biochemistry of colour variants and evaluate maternal and paternal fitness of light and dark morphs by crossing within and between morphs. Pollen colour was largely uncorrelated with floral traits (petal colour, size, nectar traits) suggesting it can evolve independently. Darker pollen grains were larger and had higher anthocyanin content (cyanidin and peonidin) which may explain why they outperform light pollen under heat stress. Overall, pollen‐related fitness metrics were greater for dark pollen, and dark pollen sires generated seeds with higher germination potential. Conversely, light pollen plants produce 61% more flowers than dark, and 18% more seeds per fruit, suggesting a seed production advantage. Results indicate that light and dark morphs may achieve fitness through different means—dark morphs appear to have a pollen advantage whereas light morphs have an ovule advantage—helping to explain the maintenance of pollen colour variation.     

Evolution and maintenance of pollen-colour dimorphisms in Nigella degenii: habitat-correlated variation and morph-by-environment interactions

Dimorphism in pollen colour is rare among flowering plants, but occurs in two geographically and morphologically distinct subspecies of Nigella degenii (Ranunculaceae). We evaluated the role of genotype-by-environment interactions in the maintenance of two pollen morphs within each of these subspecies. Morph frequencies in a number of populations were related to current habitat conditions, and an extensive common-garden experiment involving both optimal and stressful conditions (drought and nutrient deficiency) was carried out. The putatively derived (dark) pollen morph of N. degenii ssp. barbro has a higher frequency on slopes facing north or east than on slopes facing south or west. Plants of the dark morph also have a higher mortality under drought stress or nutrient deficiency. Data available for N. degenii ssp. jenny provide little evidence for habitat-correlated variation in morph frequency or morph-specific differences in fitness under optimal and stressful growth conditions. Our results suggest that morph-by-environment interactions in mortality could contribute to the maintenance of pollen-colour dimorphisms in N. degenii ssp. barbro.     

POLLEN DISCOUNTING AND THE SPREAD OF A SELFING VARIANT IN TRISTYLOUS EICHHORNIA PANICULATA: EVIDENCE FROM EXPERIMENTAL POPULATIONS

Floral traits that increase self-fertilization are expected to spread unless countered by the effects of inbreeding depression, pollen discounting (reduced outcross pollen success by individuals with increased rates of self-fertilization), or both. Few studies have attempted to measure pollen discounting because to do so requires estimating the male outcrossing success of plants that differ in selfing rate. In natural populations of tristylous Eichhornia paniculata, selfing variants of the mid-styled morph are usually absent from populations containing all three style morphs but often predominate in nontrimorphic populations. We used experimental garden populations of genetically marked plants to investigate whether the effects of population morph structure on relative gamete transmission by unmodified (M) and selfing variants (M‘) of the mid-styled morph could explain their observed distribution. Transmission through ovules and self and outcross pollen by plants of the M and M’ morphs were compared under trimorphic, dimorphic (S morph absent), and monomorphic (L and S morphs absent) population structures. Neither population structure nor floral morphology affected female reproductive success, but both had strong effects on the relative transmission of male gametes. The frequency of self-fertilization in the M' morph was consistently higher than that of the M morph under all morph structures, and the frequency of self-fertilization by both morphs increased as morph diversity of experimental populations declined. In trimorphic populations, total transmission by the M and M' morphs did not differ. The small, nonsignificant increase in selfing by the M' relative to the M morph was balanced by decreased outcross siring success, particularly on the S morph. In populations lacking the S morph, male gamete transmission by the M' morph was approximately 1.5 times greater than that by the M morph because of both increased selfing and increased success through outcross pollen donation. Therefore, gamete transmission strongly favored the M' morph only in the absence of the S morph, a result consistent with the distribution of the M' morph in nature. This study indicates that floral traits that alter the selfing rate can have large and context-dependent influences on outcross pollen donation.     

Pollination biology and the impact of floral display, pollen donors, and distyly on seed production in Arcytophyllum lavarum (Rubiaceae)

In animal-pollinated plants, two factors affecting pollen flow and seed production are changes in floral display and the availability of compatible mates. Changes in floral display may affect the number of pollinator visits and the availability of compatible mates will affect the probability of legitimate pollination and seed production. Distyly is a floral polymorphism where long-styled (pin) and short-styled (thrum) floral morphs occur among different individuals. Distylous plants frequently exhibit self and intra-morph incompatibility. Therefore changes in morph abundance directly affect the arrival of compatible pollen to the stigmas. Floral morph by itself may also affect female reproductive success because floral morphs may display differences in seed production. We explored the effects of floral display, availability of neighboring compatible mates, and floral morph on seed production in the distylous herb ARCYTOPHYLLUM LAVARUM. We found that floral display does not affect the mean number of seeds produced per flower. There is also no effect of the proportion of neighboring legitimate pollen donors on seed production in pin or thrum flowers. However, floral morphs differed in their female reproductive success and the thrum morph produced more seeds. Hand pollination experiments suggest that differences in seed production between morphs are the result of pollen limitation. Future research will elucidate if the higher seed production in thrum flowers is a consequence of higher availability of pollen donors in the population, or higher efficiency of the pin morph as pollen donor.     

The effect of protandry on siring success in Chamerion angustifolium (Onagraceae) with different inflorescence sizes

Abstract Protandry, a form of temporal separation of gender within hermaphroditic flowers, may reduce the magnitude of pollen lost to selfing (pollen discounting) and also serve to enhance pollen export and outcross siring success. Because pollen discounting is strongest when selfing occurs between flowers on the same plant, the advantage of protandry may be greatest in plants with large floral displays. We tested this hypothesis with enclosed, artificial populations of Chamerion angustifolium (Onagraceae) by experimentally manipulating protandry (producing uniformly adichogamous or mixed protandrous and adichogamous populations) and inflorescence size (two-, six-, or 10-flowered inflorescences) and measuring pollinator visitation, seed set, female outcrossing rate, and outcross siring success. Bees spent more time foraging on and visited more flowers of larger inflorescences than small. Female outcrossing rates did not vary among inflorescence size treatments. However, seed set per fruit decreased with increasing inflorescence size, likely as a result of increased abortion of selfed embryos, perhaps obscuring the magnitude of geitonogamous selfing. Protandrous plants had a marginally higher female outcrossing rate than adichogamous plants, but similar seed set. More importantly, protandrous plants had, on average, a twofold siring advantage relative to adichogamous plants. However, this siring advantage did not increase linearly with inflorescence size, suggesting that protandry acts to enhance siring success, but not exclusively by reducing between-flower interference.     

Phenological match drives pollen‐mediated gene flow in a temporally dimorphic tree

• Variation in flowering phenology is common in natural populations, and is expected to be, together with inter‐mate distance, an important driver of effective pollen dispersal. In populations composed of plants with temporally separated sexual phases (i.e. dichogamous or heterodichogamous populations), pollen‐mediated gene flow is assumed to reflect phenological overlap between complementary sexual phases. In this study, we conducted paternity analyses to test this hypothesis in the temporally dimorphic tree Acer opalus.
• We performed spatially explicit analyses based on categorical and fractional paternity assignment, and included tree size, pair‐wise genetic relatedness and morph type as additional predictors. Because differences between morphs in flowering phenology may also influence pollination distances, we modelled separate pollen dispersal kernels for the two morphs.
• Extended phenological overlap between male and female phases (mainly associated with inter‐morph crosses) resulted in higher siring success after accounting for the effects of genetic relatedness, morph type and tree size, while reduced phenological overlap (mainly associated with intra‐morph crosses) resulted in longer pollination distances achieved. Siring success also increased in larger trees.
• Mating patterns could not be predicted by phenology alone. However, as heterogeneity in flowering phenology was the single morph‐specific predictor of siring success, it is expected to be key in maintaining the temporal dimorphism in A. opalus, by promoting not only a prevalent pattern of inter‐morph mating, but also long‐distance pollination resulting from intra‐morph mating events.

     

异型花柱植物喀什补血草的传粉者功能群与花粉转移效率

异型花柱是受遗传控制的花柱多态现象, 被达尔文认为是植物通过在传粉者体表不同部位滞落花粉以促进型间花粉准确传递的一种适应。该现象虽已受到广泛关注, 但在一些花型变异较大且不稳定的传粉系统中, 不同传粉者对各花型繁殖所产生的影响仍知之甚少。该研究以分布于新疆天山南坡的一个有同长花柱共存的异型花柱植物喀什补血草(Limonium kaschgaricum)种群为研究对象, 对其花型构成及频率、传粉者及花粉转移效率等进行了调查分析。结果表明: 1)种群中除了存在雌/雄蕊长度交互对应的长(L)/短(S)花柱型花外, 还有雌/雄蕊同长的花(H型), 且各花型花的花冠口直径、花冠筒长及花粉量等参数间无差异, 但花粉纹饰和柱头乳突细胞形态具二型性。其中, H型花的花粉和柱头形态与L型花(或S型花)的一致。2)花型内和自花授粉均不亲和; 型间授粉时, 花粉和柱头形态不同的花型间亲和, 反之不亲和。3)种群内存在长/短吻两类传粉昆虫。在以短吻传粉者为主的盛花初、中期, L和H型花柱头上的异型花粉数均显著高于S型花的, 且L和S型花高位性器官间的异型花粉传递效率高于低位性器官间的; 而在以长吻传粉者为主的盛花后期, L和S型花的柱头间异型花粉数无显著差异, 且高/低位性器官间具有相同的异型花粉转移效率; 与传粉者出现时期相对应的、在花期不同阶段开放花的结实率也明显不同。4)长/短吻昆虫具明显不同的传粉功能, 短吻昆虫只能对L和H型花进行有效传粉, 且访花频率和型间花粉转移效率较低, 为低效传粉者; 而长吻昆虫对各花型均能有效传粉, 具高的访花频率和型间花粉转移效率, 为高效传粉者。因为长吻昆虫的阶段性出现所形成的不稳定传粉系统, 使低效的短吻昆虫可能会成为种群中花型变异的驱动力, 并使S型花受到更大的选择压力。H型花克服了柱头缩入的弊端, 可能会成为不稳定传粉系统下的一个替代花型而持续存在。     

The genetic basis of naturally occurring pollen color dimorphisms in Nigella degenii (Ranunculaceae)

Nigella degenii ssp. barbro and ssp. jenny differ from related taxa in being dimorphic for pollen color, with some plants having dark pollen and others light pollen. In this study we performed experimental crosses to determine whether the difference in pollen color is governed by few or many loci and whether the two subspecies utilize the same gene to control pollen color. Patterns of segregation in crosses between morphs show that dark pollen is dominant over light pollen and that a single major gene is responsible for most of the variation in pollen color. Consequently it should be relatively easy for pollen color dimorphisms to establish and spread in these subspecies. Aberrant segregation ratios were attributed to genetic factors that reduced the expression of the allele conferring dark pollen or processes that sorted between color morphs during seed development. Crosses between dark pollen plants from different subspecies showed signs of complementation in the F2 generation, but the frequency of the light morph was too low to support a model involving complementary action of recessive alleles at two separate loci. Based on this and other observations, we hypothesize that the pollen color difference is controlled by the same major locus in the two subspecies.     

云南草寇花序内不同部位的性分配

两性花植物花序内的性分配常存在差异,资源竞争、结构效应、交配环境(雌雄异熟、传粉者定向访花行为等)或授粉不均匀等几种假说可以解释这种现象。为验证上述假说,该研究以云南草寇两种表型(雄先熟型和雌先熟型)为材料,分析了其花序内不同部位(基部、中部和顶部)的每花花粉数、胚珠数、花粉/胚珠比、结实率和结籽率,花序内传粉者的定向访花行为,以及人工辅助授粉和去花处理对结实率和结籽率的影响。结果表明:两种表型花序内每花花粉数不随部位而变化,每花胚珠数、结实率和结籽率由基部到顶部依次降低,每花花粉/胚珠比由基部到顶部依次增加,表明顶部花存在偏雄的性分配。人工辅助授粉后,结实率、结籽率仍由基部到顶部依次降低,表明授粉不均匀假说不能解释云南草寇花序内不同部位结实率、结籽率的差异。去除基部和中部花后,顶部花人工辅助授粉条件下的结实率、结籽率与基部花人工辅助授粉条件下的结实率、结籽率无差异,表明云南草寇花序内不同部位结实率、结籽率的差异主要由资源竞争引起。雌先熟表型每花花粉数、花粉/胚珠比高于雄先熟表型,表明两种表型存在性分配差异。传粉者主要先访问云南草寇基部的花,然后向顶部移动。云南草寇花序内顶部偏雄的性分配可能是由资源竞争和传粉者定向访花造成的。     

Male interference with pollination efficiency in a hermaphroditic orchid

Hermaphroditism can lead to both intra‐ and intersexual conflict between male and female gender functions. However, the effect that such gender conflicts have on pollination efficiency has seldom been investigated. By artificially reducing the number of available male gametes on an individual, we quantified whether male interference with pollination efficiency occurs in the self‐compatible, moth‐pollinated orchid Satyrium longicauda. We partially emasculated S. longicauda inflorescences and compared pollination success and fecundity in these plants to intact controls. Pollen in both groups of plants was colour‐labelled so that its dispersal by pollinators could be tracked directly in the field. Intact flowers on partially emasculated inflorescences exported more pollen and received more cross‐pollen and less self‐pollen than those on intact inflorescences. Proportion of fruit set per plant was similar between the two treatments; however, fruits on partially emasculated plants had proportionally more viable seeds than those on intact controls. These results provide empirical evidence that male interference with pollination efficiency can occur in a hermaphroditic plant and that such interference can compromise fecundity. The most likely mechanism for such male interference is competition for placement on the proboscis of hawkmoth pollinators. Consequently, male competition for siring success may influence the evolution of sexual systems in hermaphroditic pollinator‐dependent plants.     

Morph‐dependent fitness and directional change of morph frequencies over time in a Dutch population of Common buzzards Buteo buteo

How genetic polymorphisms are maintained in a population is a key question in evolutionary ecology. Previous work on a plumage colour polymorphism in the common buzzard Buteo buteo suggested heterozygote advantage as the mechanism maintaining the co‐existence of three morphs (light, intermediate and dark). We took advantage of 20 years of life‐history data collected in a Dutch population to replicate earlier studies on the relationship between colour morph and fitness in this species. We examined differences between morphs in adult apparent survival, breeding success, annual number of fledglings produced and cumulative reproductive success. We found that cumulative reproductive success differed among morphs, with the intermediate morph having highest fitness. We also found assortative mating for colour morph, whereby assortative pairs were more likely to produce offspring and had longer‐lasting pair bonds than disassortative pairs. Over the 20‐year study period, the proportion of individuals with an intermediate morph increased. This apparent evolutionary change did not just arise from selection on individual phenotypes, but also from fitness benefits of assortative mating. The increased frequency of intermediates might also be due to immigration or drift. We hypothesize that genetic variation is maintained through spatial variation in selection pressures. Further studies should investigate morph‐dependent dispersal behaviour and habitat choice.     

Pollinators differ in their contribution to the male fitness of a self-incompatible composite

Premise

Reproductive fitness in plants is often determined by the quantity and quality of pollen transferred by pollinators. However, many fitness studies measure only female fitness or rely on proxies for male fitness. Here we assessed how five bee taxon groups affect male fitness in a prairie plant by quantifying pollen removal, visitation, and siring success using paternity assignments and a unique pollinator visitation experiment.

Methods

In Echinacea angustifolia, we measured per-visit pollen removal for each pollinator taxon and estimated the number of pollen grains needed for successful ovule fertilization. Additionally, we directly measured pollinator influence on siring by allowing only one bee taxon to visit each pollen-donor plant, while open-pollinated plants acted as unrestricted pollen recipients. We genotyped the resulting offspring, assigned paternity, and used aster statistical models to quantify siring success.

Results

Siring success of pollen-donor plants differed among the five pollinator groups. Nongrooming male bees were associated with increased siring success. Bees from all taxa removed most of the flowering head's pollen in one visit. However, coneflower-specialist bee Andrena helianthiformis removed the most pollen per visit. Female fitness and proxy measures of male fitness, such as pollinator visitation and pollen removal, did not align with our direct quantifications of male fitness.

Conclusions

Our results illustrate the need for more studies to directly quantify male fitness, and we caution against using male fitness proxy measures. In addition, conservation efforts that preserve a diverse pollinator community can benefit plants in fragmented landscapes.

     

Spatio-temporal variation in pollen limitation and reproductive success of two scape morphs in Primula farinosa

In plant populations where reproductive output is limited by pollinator visitation, plants with attractive floral displays should have a selective advantage. We examined the effect of inflorescence height on pollination success in Primula farinosa, which is dimorphic for scape length. To test the hypothesis that fruit and seed initiation are more strongly pollen-limited in the short-scaped than in the long-scaped morph, and that this difference is affected by spatio-temporal variation in pollen limitation, we conducted a hand-pollination experiment in four populations over 2 yr. Pollen limitation of fruit initiation varied among populations and years, and was stronger in the short-scaped than in the long-scaped morph. The results suggest that interactions with pollinators will need to be considered for a full understanding of the maintenance of this striking polymorphism. The study also shows that, although pollen limitation is likely to vary in space and time in many plant species, such variation is not necessarily associated with variation in selection on floral characters.     

Pollinator response to flower color polymorphism and floral display in a plant with a single-locus floral color polymorphism: consequences for plant reproduction

Variation in flower color, particularly polymorphism, in which two or more different flower color phenotypes occur in the same population or species, may be affected or maintained by mechanisms that depend on pollinators. Furthermore, variation in floral display may affect pollinator response and plant reproductive success through changes in pollinator visitation and availability of compatible pollen. To asses if flower color polymorphism and floral display influences pollinator preferences and movements within and among plants and fitness-related variables we used the self-incompatible species Cosmos bipinnatus Cav. (Asteraceae), a model system with single-locus flower color polymorphism that comprises three morphs: white (recessive homozygous), pink (heterozygous co-dominate), and purple (dominant homozygous) flowers. We measured the preferences of pollinators for each morph and constancy index for each pollinator species, pollination visitation rate, floral traits, and female fitness measures. Flower color morphs differed in floral trait measures and seed production. Pollinators foraged nonrandomly with respect to flower color. The most frequent morph, the pink morph, was the most visited and pollinators exhibited the highest constancy for this morph. Moreover, this morph exhibited the highest female fitness. Pollinators responded strongly to floral display size, while probed more capitulums from plants with large total display sizes, they left a great proportion of them unvisited. Furthermore, total pollinator visitation showed a positive relation with female fitness. Results suggest that although pollinators preferred the heterozygous morph, they alternate indiscriminately among morphs making this polymorphism stable.     

CONTRIBUTION OF CRYPTIC INCOMPATIBILITY TO THE MATING SYSTEM OF EICHHORNIA PANICULA TA (PONTEDERIACEAE)

Tristylous populations of the annual aquatic Eichhornia paniculata have high levels of outcrossing and intermorph mating despite being fully self- and intramorph compatible. Experimental studies of pollen germination, ???pollen-tube growth, and pollinations with mixtures of genetically marked pollen were used to determine whether postpollination processes contribute to the observed mating patterns. Differences in pollen germination were small and did not contribute to differences in pollen siring ability. The fraction of pollen tubes first entering the ovary, however, was greater for legitimate outcross pollen than for either of the other two pollen types (self or outcross illegitimate pollen) in all recipient morphs. Moreover, legitimate pollen had higher siring success when in competition with illegitimate pollen types (self or outcross) in each recipient style morph. The ranking of pollen performance for different pollen-style combinations was the same for both the pollen-tube growth and marker-gene experiments indicating that differences in pollen-tube growth rate are the principal cause of differences in pollen siring ability. Cryptic incompatibility in E. paniculata may represent a weak heteromorphic incompatibility system because the observed patterns of pollen-tube growth parallel pollen-tube growth and seed-set patterns that occur in related species with strong trimorphic incompatibility. The ability to produce mostly outcrossed progeny when pollinators are abundant, but to reliably produce seed under a variety of environmental and demographic conditions may be favored in E. paniculata because of its colonizing life history and occurrence in ephemeral habitats. Cryptic incompatibility may be more likely to occur in species subject to wide fluctuations in population size and levels of pollinator service.     

Differential siring success of Pgi genotypes in Clarkia Unguiculata (Onagraceae)

Competition among pollen grains for the fertilization of ovules can play an important role in determining the male and female reproductive success of flowering plants. To examine the influence of pollen-donor genotype on male reproductive success, hand-pollinations were conducted on Clarkia unguiculata and the siring success of pollen-donor plants was compared between donors homozygous for different allelomorphs of the allozyme PGI (phosphoglucoisomerase). Donors homozygous for the B allele sired more seeds than C-allele donors. Single-donor crosses indicated that C-donor-sired seeds are aborted more often than are B-donor-sired seeds, suggesting that the B-allele donor's advantage in mixed pollinations was a result of differential abortion. A negative relationship between pollen load and the siring success of B-allele donors implies that pollen from B-allele donors has reduced performance relative to C-allele donors when pollen loads are high. These data demonstrate consistent differences in siring success between individuals homozygous for different alleles at a single locus and suggest that variation at the Pgi locus may be maintained by a post-pollination trade-off.     

Disassortative mating prevails in style‐dimorphic Narcissus papyraceus despite low reciprocity and compatibility of morphs

Evolution to reduce inbreeding can favor disassortative (intermorph) over assortative (intramorph) mating in hermaphroditic sexually polymorphic plant species. Heterostyly enhances disassortative pollination through reciprocal placement of stigmas and anthers of morphs and appropriate pollinators. Stylar dimorphism in which there is not reciprocal anther placement may compromise disassortative mating, particularly when there is not intramorph incompatibility. Variable rates of disassortative mating along with differential female fecundity or siring success among floral morphs could lead to variation in morph ratio. We investigated mating patterns, female fecundity, and siring success of style‐length morphs in Narcissus papyraceus, a self‐incompatible but morph‐compatible species with dimorphic (long‐ and short‐styled) and monomorphic (long‐styled) populations in central and north regions of its range, respectively. We established experimental populations in both regions and exposed them to ambient pollinators. Using paternity analysis, we found similar siring success of morphs and high disassortative mating in most populations. Female fecundity of morphs was similar in all populations. Although these results could not completely explain the loss of dimorphism in the species’ northern range, they provided evidence for the evolutionary stability of stylar dimorphism in N. papyraceus in at least some populations. Our findings support the hypothesis that prevailing intermorph mating is key for the maintenance of stylar dimorphism.     

Discovery of androecium color polymorphism in Epimedium pubescens with habitat preference of anther/pollen color in the genus

Aims Interspecific and intraspecific variation in flower color in natural populations provides an opportunity for us to understand the evolution and maintenance of diversity of floral traits. Compared to corolla color, little is known about the color polymorphism of sexual organs in flowering plants. To explore evolutionary transitions of androecium color and polymorphism within species, interspecific and intraspecific variation in androecium (anther and pollen) color in the genus Epimedium (Berberidaceae) was investigated.Methods To explore the geographical patterns of anther/pollen color variation in Epimedium species, data of 45 species were collected and their phylogeny was constructed based on available DNA sequences. To investigate whether intraspecific variation in androecium color relates to habitat preference, three environmental factors were measured in the field population of Epimedium pubescens in northeastern Sichuan, China, which plants had green or yellow androecia. Vegetative and reproductive traits of this species were compared between the two color morphs.Important findings Androecium (anther and pollen) color polymorphism in field populations of Epimedium pubescens is reported here where nine populations are monomorphic with a green androecium but three populations are dimorphic with individuals having either a green or a yellow androecium. Inflorescence stalk height, stalk diameter, leaf number, flower number and spur length (as well as spur and nectar volume) were not significantly different between two morphs. Compared to the yellow morph, the green morph had relatively larger leaves and anthers, but smaller sepals. The green morph produced more pollen and larger seeds, but the same number of ovules. Seed set was not significantly different between green and yellow morph. Investigations of environmental factors in the color dimorphic populations of E. pubescens indicated that the green morph was more likely to occur in habitats with relatively lower light intensity. The distribution survey of 45 Epimedium species showed that species with a green androecium tended to appear at lower elevations. Comparative phylogenetic analysis showed that transitions from yellow to a green androecium or to androecial color dimorphism occurred at least seven times. This genus, characterized by anther color diversity and containing some species with anther color polymorphism, provides a model system in which to study the evolution and maintenance of colorful sexual organs in flowering plants.     

Plumage polymorphism and fitness in Swainson’s hawks

We examine the maintenance of a plumage polymorphism, variation in plumages among the same age and sex class within a population, in a population of Swainson’s Hawks. We take advantage of 32 years of data to examine two prevalent hypotheses used to explain the persistence of morphs: apostatic selection and heterozygous advantage. We investigate differences in fitness among three morph classes of a melanistic trait in Swainson’s Hawks: light (7% of the local breeding population), intermediate (57%) and dark (36%). Specifically, we examined morph differences in adult apparent survival, breeding success, annual number of fledglings produced, probability of offspring recruitment into the breeding population and lifetime reproductive success (LRS). If apostatic selection were a factor in maintaining morphs, we would expect that individuals with the least frequent morph would perform best in one or more of these fitness categories. Alternatively, if heterozygous advantage played a role in the maintenance of this polymorphism, we would expect heterozygotes (i.e. intermediate morphs) to have one or more increased rates in these categories. We found no difference in adult apparent survival between morph classes. Similarly, there were no differences in breeding success, nest productivity, LRS or probability of recruitment of offspring between parental morph. We conclude that neither apostatic selection nor heterozygous advantage appear to play a role in maintaining morphs in this population.